1. Field of the Invention
The invention relates to a record-reproduction apparatus which records or reproduces data signals such as digital audio signals from a recording medium.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating prior art configuration for duplicating audio signals (e.g., audio signals of music). In the figure, 43 designates a compact disk player (hereinafter abbreviated as "CD player"), and 44 designates a tape recorder. Conventionally, the duplication of audio signals requires such a configuration in which audio signals recorded on, for example, a compact disk (hereinafter, abbreviated as "CD") are reproduced by the CD player 43 and the reproduced audio signals are recorded by the tape recorder 44.
The duplication of audio signals using such a prior art method requires a period which is equal to the reproduction period of the audio signals. When the duplication is to be conducted within a shorter period (for example, a half of the reproduction period), the following steps must be performed. When the audio signals recorded on a CD are reproduced by the CD player 43 at a speed (two-time speed) which is two times the normal speed, the reproduced audio signals are recorded by the tape recorder 44 at the two-time speed. Therefore, the CD player 43 must be provided with a mechanism for reproducing at the two-time speed audio signals recorded on a CD, and additional circuits for a digital signal processing and the tape recorder 44 must be provided with a mechanism and circuits for recording signals at the two-time speed. This results in a problem in that the structure of a duplication apparatus is complicated. Furthermore, there is another problem in that, even when audio signals are to be duplicated at a high speed, the speed is limited to the two-time speed at the maximum.
Recently, digital audio apparatuses using an optical disk have been developed. A CD is a well known recording medium that can be used in a system of the reproduction-only type in which the user cannot record data on a recording medium. Known recording media on which the user can record data include a write-once optical disk which is called a "CD-R" and on which the user can record data only one time. Furthermore, researchers are developing optical disk apparatuses of the magnetooptical type in which the user can record data on a medium any number of times. An example of such an apparatus is an MD (mini-disk) system which is disclosed in "Feature and view of mini-disk (MD) system developers tell." written in PP.152-155, December, 1991, Radio Technic or "Mini-disk is realized by magnetooptical record and data compression technic" written in pp.160-168, Dec. 5, 1991, Nikkei Electronics.
In an MD system, data-compressed audio signals are magnetooptically recorded on or reproduced from a disk. In such a disk, a guide groove for performing the tracking control is previously formed, and continuous address data are previously written in the guide groove over the whole area of the disk. Therefore, irrespective of the presence of recorded signals, such a disk can be subjected to a search operation.
FIG. 2 is a block diagram of an MD system. In the figure, 1 designates a 2-channel audio signal input terminal, 2 designates an analog/digital (A/D) converter, 3 designates an encoder, 4 designates a buffer memory for recording, 5 designates an ECC encoder which generates error-correcting codes and adds them to signals, 6 designates a modulator, 7 designates a record head driving circuit, 8 designates a magnetic record head, 9 designates a disk, 10 designates an optical pickup, 11 designates a reproduction amplifier, 12 designates a demodulator, 13 designates an error controller, 14 designates a buffer memory for reproduction, 15 designates a decoder, 16 designates a digital/analog (D/A) converter, 17 designates a 2-channel audio signal output terminal, 18 designates an address decoder, 19 designates a microcomputer, 20 designates a servo circuit, 21 designates a motor, 22 designates input keys, and 23 designates a display circuit.
FIG. 3 is a timing chart illustrating the signal processing in the record and reproduction processes. Referring to FIGS. 2 and 3, the operation of the MD system will be described. Analog audio signals supplied through the audio signal input terminal 1 are sampled in the A/D converter 2 to be converted into digital signals. The digital signals are then subject to the audio signal compression and encoding process in the encoder 8 so that the data amount is reduced to about one fifth of that of the original signal.
The encoded signals are once stored in the buffer memory 4, and then intermittently read out from the buffer memory 4 at a signal rate which is equal to that before the encoding. The ECC encoder 5 conducts the interleave process for rearranging the order of signals in order to disperse possible errors in the reproduction, and also a process of generating error-correcting codes and adding them to signals. The modulator 6 performs a modulation so that the energy is concentrated on the frequency band suitable for record and reproduction and that its own clock can be extracted during the reproduction process. The signals are supplied through the record head driving circuit 7 to the magnetic record head 8 which in turn magnetooptically records the signals on the disk 9. The recording is conducted in accordance with a modulation signal (FIG. 3(c)) which is intermittently supplied. As shown in FIG. 3(d), the record state and the record pause state are alternately repeated, the last address of the portion where data have been recorded is searched before starting the recording, and data are recorded at addresses subsequent to the searched address.
In the reproduction process, signals written on the disk 9 are read out on the basis of the light beam emitted from the optical pickup 10 toward the disk 9 and reflected therefrom. The optical data are converted into electric signals by the optical pickup 10, and then supplied to the reproduction amplifier 11. The signals amplified by the reproduction amplifier 11 are supplied to the demodulator 12 and demodulated therein so that the original signal sequence is restored.
On the other hand, the output of the reproduction amplifier 11 is supplied also to the address decoder 18. The address decoder 18 reproduces signals of continuous addresses of the whole area of the disk 9 in order to pick out data contained in the optical spot groove which is previously engraved on the disk 9, and detects the wobbling of the guide grooves to obtain tracking information. The tracking information is supplied to the servo circuit 20 so that the optical pickup 10 is subjected to the tracking servo control so as to scan a predetermined guide groove, and that the motor 21 is subjected to the servo control to maintain a constant linear velocity of the disk rotation, thereby making the period of the wobbling of the guide grooves constant.
In a similar manner as the writing process in the record process, the process of reading a signal from the disk 9 is intermittently conducted, and, as shown in FIGS. 3(e) and 3(f), the reproduction state and the reproduction pause state are alternately repeated. The signals demodulated by the demodulator 12 are subjected in the error controller 13 to the error detection and error correction processes and the deinterleave process by which the signal sequence is returned to the original one. Then the signals are supplied to the buffer memory 14, and read out therefrom are provided to the decoder 15. Generally, the inputs to the buffer memory 14 are controlled so that the amount of signals stored in the memory is kept greater than a predetermined value. More specifically, as shown in FIG. 3(h), when data stored in the buffer memory 14 equals the memory capacity, the data input is halted and the reproduction pause state is set, and, when the data amount of the buffer memory 14 becomes less than a level indicated by a, the portion of the disk 9 subsequent to that from which data have been read out is searched and the reproduction process is conducted on the searched portion to supply data to the buffer memory 14. Therefore, the buffer memory 14 always stores at least data of the amount a even when, for example, the optical pickup 10 is erroneously caused to jump by disturbance. Therefore, the location at which the optical pickup 10 was positioned before the jump can be searched while the data stored in the buffer memory 14 are read out, so that the reproduction is conducted without interruption.
The audio signals which have been restored by the decoder 15 so as to have the data amount before encoding are converted into analog signals by the D/A converter 16 and then output through the audio signal output terminal 17. From the address decoder 18, the microcomputer 19 receives address signals engraved in the guide groove of the disk, and address signals recorded in correspondence with the audio signals. The microcomputer 19 further receives input signals from the external input keys 22, and controls the whole system. The microcomputer 19 drives the display circuit 23 to perform the display to the outside.
Also in such a disk device in which the user can record data (hereinafter, referred to as "recordable disk device"), in a similar manner as a CD, the start times of the programs are recorded in a TOC (Table Of Contents) so that the data are used for a program search, etc. during the reproduction process. Since the user can freely record data in the disk, however, the management and operation of the TOC are more difficult than those in a CD. For example, the reproduction of a CD does not produce a sense of incongruity because the time periods of so-called intermusic portions disposed between programs are substantially constant. By contrast, in a recordable disk device, the time periods of intermusic portions are divergent in length, thereby producing a problem in that a silent period corresponding to an intermusic portion may continue for a long time. When data are to be additionally recorded on a disk having a recorded portion, it is desirous to record the data efficiently using the unrecorded portion. In such a recordable disk device, accordingly, a TOC must be effectively used in both the record and reproduction processes.
Furthermore, a conventional system is provided with a measure of preventing the reproduction from being interrupted even when an optical pickup is accidentally caused to jump by a shock during the reproduction process, so that it is suitable for the use in a portable system or a system mounted in a car. In a general fixed system, however, an optical pickup is hardly caused to erroneously jump by a shock. Accordingly, it is desired to apply to another use the technique by which continuous signals are compressed and intermittently recorded and reproduced, thereby providing a new function.